We're looking for a user researcher to understand the needs of developers and designers. Is this you or someone you know? Check out the post: https://mzl.la/2IGzdXS

The static Reflect.preventExtensions() method prevents new properties from ever being added to an object (i.e. prevents future extensions to the object). It is similar to Object.preventExtensions(), but with some differences.




The target object on which to prevent extensions.

Return value

A Boolean indicating whether or not the target was successfully set to prevent extensions.


A TypeError, if target is not an Object.


The Reflect.preventExtensions method allows you to prevent new properties from ever being added to an object (i.e. prevents future extensions to the object). It is the same method as Object.preventExtensions().


Using Reflect.preventExtensions()

See also Object.preventExtensions().

// Objects are extensible by default.
var empty = {};
Reflect.isExtensible(empty); // === true

// ...but that can be changed.
Reflect.isExtensible(empty); // === false

Difference to Object.preventExtensions()

If the first argument to this method is not an object (a primitive), then it will cause a TypeError. With Object.preventExtensions(), a non-object first argument will be coerced to an object at first.

// TypeError: 1 is not an object

// 1


Specification Status Comment
ECMAScript 2015 (6th Edition, ECMA-262)
The definition of 'Reflect.preventExtensions' in that specification.
Standard Initial definition.
ECMAScript Latest Draft (ECMA-262)
The definition of 'Reflect.preventExtensions' in that specification.

Browser compatibility

FeatureChromeEdgeFirefoxInternet ExplorerOperaSafari
Basic support491242 No3610
FeatureAndroid webviewChrome for AndroidEdge mobileFirefox for AndroidOpera AndroidiOS SafariSamsung Internet
Basic support4949 Yes4236105.0

See also

Document Tags and Contributors

Last updated by: wbamberg,